Basic Properties of the Nervous System and Arousal Model in the Light of Current Neuropsychophysiology

Abstract

To approach the question of the basic properties of the nervous system and their relevance to current neurophysiology and psychophysiology, a preliminary reference to the notion of the “conceptual nervous system” is required. According o the interpretation formulated by Skinner (1938), Pavlov gave a “conceptual” description of the brain functions inferred from behavior, instead of a description founded on direct investigation of these functions. Indeed, Pavlov developed the theory of higher nervous activity through a long and insightful series of behavioral experiments, without trying to directly study the nervous activity involved in the dynamics of the conditioned reflex. This meant a clear rejection of contemporary physiological and neurological methods/like the ablations of brain tissue or electrophysiological recordings. However, that refusal was not simply a question of methodological choice. Pavlov maintained that the complexity of the nervous activity involved in behavior called for more appropriate methods than those used in brain research at that time. For a molecular investigation of single nervous units, current neurophysiological methods might be suitable. For the investigation of the brain in its behavioral functions, another methodology would be needed to meet such a complexity. The experiment had to be designed in order to exhibit the integrated activity of the brain during the dynamics of the conditioned reflex, and, correspondingly, an integrated behavioral process, just like the conditioned reflex, had to be investigated, rather than its single fragments. Needless to say, the Pavlovian approach implied a new terminology to illustrate the integrated brain dynamics that had not been previously investigated by other neurophysiologists. It is known that Pavlov used old terms for new concepts (for example, the term inhibition had a particular meaning in the Pavlovian theory, that was very different from the current meaning in neurophysiology). Undoubtedly, this renewed terminology often did not do justice to the innovation of Pavlov’s concepts. In this sense, the theory of the four types of nervous systems might seem old hat (Hippocrates’ four types of temperament) in the new form represented by the physiological framework. However, Pavlov expressed in very clear terms the idea that a theory of higher nervous activity involved in behavior should take into consideration the wide variety of individual differences observed. For this reason, a theory of brain activity at the behavioral level of complexity had to comprehend individual differences and to give a physiological explanation.